The following is a tabulation of some prior art that presently appears relevant:
Pat. No.Kind CodeIssue DatePatentee5,256,5011993 Oct. 26Hasvold et al.5,405,7171995 Apr. 11Hasvold5,427,8711995 Jun. 27Garshol et al.4,822,6981989 Apr. 18Jackovitz et al.9,130,225B22015 Sep. 08Sun et al.4,522,8971985 Jun. 11Walsh